When I have an SVI frame serial number 38SUPER, the clerk at Four Seasons wanted me to take the transfer without a 4473 or FA10 since it was "Not a frame" (the SVI frame does not have the grip but is a rail assembly). He insisted 38SUPER was a caliber designation and the unit did not have a serial number.
I finally convinced him, which saved me an urgent call from Carl to get my butt back to the shop.
I like the "caliber is serial number" trick since it is "cool", but nor personalized and of no interest to the next owner.
(that person no longer works a 4 Seasons)